The present invention relates to improvements in multi-stage centrifugal pumps, especially submersible motor pumps or sump pumps. More particularly, the invention relates to improvements in the construction and assembly of pump stages in such pumps. Still more particularly, the invention relates to improvements in means for and in the manner of journalling the rotor of a multi-stage centrifugal pump, especially a multi-stage submersible motor pump, wherein the components of stages consist of or include synthetic plastic material.
It is known to produce the casings and impellers of stages in a centrifugal pump of a synthetic plastic material. Such parts of the pump stages are lightweight, resistant to corrosion, relatively inexpensive and can be mass-produced by resorting to any one of several well known techniques. However, the utilization of synthetic plastic parts in centrifugal pumps also presents several still unsolved problems, particularly as regards proper assembly and centering of rotary components and especially if it is desired to construct a compact centrifugal pump whose bearings are confined in the interior of the pump body. Such positioning of bearings is advantageous because the bearings can be lubricated by the conveyed fluid. In presently known centrifugal pumps of the just outlined character, the bearings consist of corrosion-resistant metallic material and each bearing is confined in a discrete housing. The space requirements of the housings for metallic bearings render it necessary to employ a relatively long pump shaft which extends through the stages as well as through the housings which alternate with the casings of neighboring stages.
Additional problems arise when the synthetic plastic parts of the stages are produced by mass-manufacturing techniques which invariably result in at least some deviations of dimensions of such parts from an optimum value. In many instances, the plastic parts (especially the casings of the pump stages) are produced with considerable tolerances and are loosely stacked in the pump body to be secured thereto (against rotation with the impellers and with the pump shaft) by resorting to simple and inexpensive rotation-preventing devices. This often results in misalignment of central openings of neighboring casings. If the rotor of such multi-stage pump is not centered with an extremely high degree of precision, i.e., in the absence of accurately machined and hence expensive bearings, the impellers are likely to rub against the respective casings when the pump is in use. This entails pronounced wear and reduces the useful life of the pump. Moreover, frictional engagement between the rotor and stator of a multi-stage pump wherein the stationary and rotary parts consist of synthetic plastic material is likely to generate sufficient heat to cause the rotary parts to become welded to the stationary parts. In order to prevent the development of such permanent bonds, many presently known centrifugal pumps which utilize synthetic plastic parts are equipped with metallic bearing rings which are interposed between the rotor and the stator. The bearing rings are used as a substitute for or in addition to the aforementioned bearings for the pump shaft.